Generally, a rear subframe (having the same meaning as “rear suspension cross member”) for supporting a rear suspension has right and left side member segments and front and rear cross member segments. As an automotive rear vehicle body structure comprising such a rear subframe, there have been known various structures as illustrated in FIGS. 16 to 20.
A conventional structure (Patent Document 1) schematically illustrated in FIG. 16 in the form of a bottom view comprises a subframe 80 having right and left side member segments 81, 81 and front and rear cross member segments 82, 83, wherein front and rear fixing sections 81a, 81b provided in respective front and rear regions of each of the right and left side member segments 81, 81 are coupled to a respective one of rear side frames 84, 84, and a front portion 81c of each of the right and left side member segments 81, 81 is coupled to a vehicle-body cross member 85 through a respective one of extension members 86, 86.
In FIG. 16, the side member segment 81 is curved inwardly in a vehicle width direction to have an approximately circular arc shape, in top plan view. This curved structure is intended to ensure an installation space for a suspension spring in order to support the suspension spring by a base of the rear side frame 84, and to increase an arm length to suppress a change in suspension geometry (change in toe angle, etc.) due to an up-and-down movement of a rear wheel 87.
In FIG. 16, the reference code 88 indicates a front lower arm, and the reference code 89 indicates a rear lower arm. Further, in the figures, the arrowed line F indicates a vehicle forward direction, and the arrowed line R indicates a vehicle rearward direction.
The conventional structure illustrated in FIG. 16 has the following problems.
First, a distance between the front and rear fixing sections 81a, 81b of the side member segment 81 is relatively long and curved. Thus, in order to ensure rigidity against an input of lateral force, it is necessary to increase a plate thickness of the side member segment 81, resulting in an increase in weight.
Further, in the event of a rear collision, a rear impact load received by a rear region of the rear side frame 84 is concentrated on a front region of the rear side frame 84, as indicated by the arrowed line in FIG. 16. This causes a problem of an increase in amount of deformation in members around a side sill located forward of the rear side frame 84.
Besides, a distance between the front fixing section 81a and a support section 88a for the front lower arm 88 is relatively long, which is disadvantageous in terms of rigidity.
Moreover, the front portion 81c of the side member segment 81 is connected to the vehicle-body cross member 85 through the extension member 86, so that rigidity of the subframe 80 is enhanced somewhat. However, an increase in length of the extension member 86 gives rise to a problem of causing the extension member 86 to more easily undergo deformation, and of increases in required installation space and weight of the extension member 86.
A conventional structure (Patent Document 2) schematically illustrated in FIG. 17 in the form of a bottom view comprises a subframe 80A having right and left side member segments 81, 81 and front and rear cross member segments 82, 83, wherein front and rear fixing sections 81a, 81b provided in respective front and rear regions of each of the right and left side member segments 81, 81 are coupled to rear side frames 84, 84. Further, the side member segment 81 is formed to be curved inwardly in a vehicle width direction to have an approximately circular arc shape, in top plan view, for the same purpose as that of the conventional structure in FIG. 16.
In FIG. 17, each of the side member segments 81, 81 is formed to be curved inwardly in the vehicle width direction, and the front fixing section 81a is coupled to the rear side frame 84. Thus, a front region of the subframe 80A is strongly supported by the rear side frame 84 which is a vehicle-body strength member extending in a front-rear direction, and the side member segment 8 becomes more likely to undergo deformation. This has been considered to be desirable in terms of coupling strength between the subframe 80A and a vehicle body and further in terms of suppression of a forward displacement of the subframe 80A during a rear collision.
However, as with the conventional structure in FIG. 16, the conventional structure illustrated in FIG. 17 is incapable of shortening a distance between the front fixing section 81a and a support section 88a for the front lower arm 88, which is disadvantageous in terms of rigidity.
As above, except for the point about the extension member 86, the conventional structure illustrated in FIG. 17 has the same problem as those in the conventional structure in FIG. 16. In FIG. 17, the same element or component as that in FIG. 16 is assigned with the same reference numeral or code.
A conventional structure (Patent Document 3) schematically illustrated in FIG. 18 in the form of a bottom view comprises a subframe 90 having right and left side member segments 81, 81 and front and rear cross member segments 82, 83, wherein: each of the side member segments 81, 81 is configured such that a front fixing section 81a thereof is coupled to a vehicle-body cross member 85, and a rear end of each of the side member segments 81 is welded and fixed to the rear cross member segment 83; and fixing sections 83b, 83b provided at respective opposite ends of the rear cross member segment 83 are coupled, respectively, to rear side frames 84, 84.
In the conventional structure illustrated in FIG. 18, each of front and rear ends of the side member segment 81 having a crank-like shape is located spaced apart from the rear side frame 84, inwardly in a vehicle width direction. Thus, during input of a rear impact load into the rear side frame 84, the rear impact load is transmitted to the vehicle-body cross member 85 via the crank-like shaped side member segment 81. However, the rear end of the side member segment 81 is not directly coupled to the rear side frame 84, which is disadvantageous in terms of distribution of a rear impact load.
Moreover, a distance between the front fixing section 81a and a support section 88a for a front lower arm 88 is relatively long, which is disadvantageous in terms of rigidity. In FIG. 18, the same element or component as that in FIG. 16 is assigned with the same reference numeral or code.
A conventional structure schematically illustrated in FIG. 19 in the form of a bottom view comprises a subframe 91 having right and left side member segments 81, 81 and front and rear cross member segments 82, 83, wherein fixing sections 82a, 82a provided at respective opposite ends of the front cross member segment 82 are coupled, respectively, to rear side frames 84, 84, and fixing sections 83a, 83a provided at respective opposite ends of the rear cross member segment 83 are coupled, respectively, to the rear side frames 84, 84.
In the conventional structure illustrated in FIG. 19, in the event of a rear collision, a rear impact load received by a rear region of the rear side frame 84 is concentrated on a front region of the rear side frame 84, as indicated by the arrowed line in FIG. 19, which is disadvantageous in terms of distribution of the rear impact load. Moreover, a distance between the front fixing section 82a and a support section 88a for the front lower arm 88 is relatively long, which is disadvantageous in terms of rigidity. In FIG. 19, the same element or component as that in FIGS. 16 to 18 is assigned with the same reference numeral or code.
A conventional structure schematically illustrated in FIG. 20 in the form of a bottom view comprises a subframe 92 having right and left side member segments 81, 81 and front and rear cross member segments 82, 83, wherein fixing sections 82a, 82a provided at respective opposite ends of the front cross member segment 82 are coupled, respectively, to rear side frames 84, 84, and fixing sections 81b, 81b provided at respective rear ends of the right and left rear side member segments 81, 81 are coupled, respectively, to the rear side frames 84, 84.
In the conventional structure illustrated in FIG. 20, in the event of a rear collision, a rear impact load received by a rear region of the rear side frame 84 is concentrated on a front region of the rear side frame 84, as indicated by the arrowed line in FIG. 20, which is disadvantageous in terms of distribution of the rear impact load. Moreover, a distance between the front fixing section 82a and a support section 88a for the front lower arm 88 is relatively long, which is disadvantageous in terms of rigidity. In FIG. 20, the same element or component as that in FIGS. 16 to 19 is assigned with the same reference numeral or code.